1. Field of the Invention
The present invention relates to a location system, a location method, and a mobile terminal. More particularly, the present invention relates to a location system and a location method to identify the position of a mobile terminal that can communicate based on a repeater installed in a radio zone, and such a mobile terminal.
2. Description of the Background Art
As an example of a zone communication system that allows communication based on repeaters provided in a plurality of radio zones respectively, a small zone radio communication system such as a PHS (Personal Handyphone System) is known.
The PHS portable terminal representative of a mobile terminal in a small zone radio communication system is used as a cordless telephone at home. It can also be carried outside to be connected to public and digital networks via indoor or outdoor public repeaters and the like. It can be used literally as a handy portable telephone. The PHS greatly differs from the existing cellular type system in that the PHS employs the small zone system.
Conventionally, a system of identifying the position of a mobile terminal is proposed according to the received electric field intensity of the radio wave of the repeater in the neighborhood of the mobile terminal that is transmitted therefrom and the identification code of the repeater, taking advantage of the feature that the radio zone of the PHS is of a small area.
However, there is a limit in the accuracy of identifying the position of the mobile terminal according to the repeater present in a radio zone how small the area may be. In order to improve the accuracy of identifying the position, the radio zone must be made smaller and the number of repeaters increased. However, this causes a great economical burden since the line facility and the like will be required for the repeaters to allow transmission/reception of information with the control station. Furthermore, if the number of repeaters is increased, the load on the control station to coordinate the repeaters becomes heavier to cause the possibility of disabled control.
In the case of a location system that uses the portable terminal of the PHS employed as a private extension within a building or the like, a possible consideration is to install many private repeaters in the building to improve the accuracy of identifying the position. However, a PBX of a great line capacity will be required as the number of repeaters is increased. There is also the problem that the economical burden is great. Furthermore, the installation cost to connect the line of each repeater to the PBX will be required. Thus, the economical burden will become greater in proportion to the increase in the number of repeaters.
In view of the foregoing, an object of the present invention is to improve the accuracy of identifying the position of a mobile terminal with the minimum cost.
According to an aspect of the present invention, a location system for identifying the position of a mobile terminal that can communicate based on a repeater installed in a radio zone, includes: a plurality of transmitter units installed around the mobile terminal apart from the repeater to send transmitter unit identification information that allows identification of each transmitter unit to the mobile terminal by a wave of a predetermined transmission output; a received field intensity measurement unit that can measure the received field intensity at the mobile terminal from the plurality of transmitter units for every different transmitter unit; and a position identify unit identifying the position of the mobile terminal according to the measured result of the received field intensity measurement unit.
According to another aspect of the present invention, a location method for identifying the position of a mobile terminal that can communicate based on a repeater provided in a radio zone, includes the steps of: sending from a plurality of transmitter units installed around the mobile terminal apart from the repeater transmitter unit identification information that can identify each of the plurality of transmitter units to the mobile terminal by a wave of a predetermined transmission output; measuring the received field intensity at the mobile terminal from the plurality of transmitter units for every different transmitter unit; and identifying the position of the mobile terminal according to the measured received field intensity.
According to a further aspect of the present invention, a mobile terminal that can communicate based on a repeater provided in a radio zone, includes: a received field intensity measurement unit measuring the received field intensity of a wave sent from a plurality of transmitter units installed around the mobile terminal apart from the repeater for every different transmitter unit; and a memory unit for storing the measured result of the received field intensity measurement unit.
Thus, the main advantage of the present invention is that a great number of repeaters to improve the accuracy for identifying the position of a mobile terminal does not have to be installed, and that the accuracy of identifying the location can be improved with the minimum cost by taking advantage of the received field intensity of the plurality of transmitter units installed around the mobile terminal apart from the repeater.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.